A variety of situations exist in which users desire access to time-ordered data, and prefer to begin utilizing that data as soon as possible after they have entered a request for the data. One example is the reproduction of streaming media data, such as a video presentation or a musical rendition. In the case of a video, for instance, a television system subscriber may desire to view a particular movie that is being broadcast by a cable or satellite television network.
In a conventional television system, the subscriber is required to wait until the scheduled time at which the movie is to be broadcast before it is possible to begin viewing it. For instance, a given movie may be repetitively broadcast on a particular channel every two hours. If the subscriber becomes aware of the movie's availability one half hour after the most recent broadcast has begun, it is necessary to wait an hour and a half before the movie can be viewed in its entirety from start to finish. As an alternative, the subscriber could choose to ignore the first half hour that was missed, and view the remaining portion of the movie. In many situations, however, this alternative is unacceptable, particularly where the initial portion of the movie is essential to an understanding of events that occur later in the movie.
To alleviate this situation, different approaches have been employed to reduce the time that a subscriber must wait until the next instance at which the beginning of the movie becomes available. In general, the maximum potential waiting period is reduced by allocating a greater amount of bandwidth, e.g., number of channels, to the movie. In certain situations, the available bandwidth is sufficient to provide true video-on-demand to all viewers, whereby the movie begins to be transmitted in its entirety to any viewer immediately upon receiving a request for the movie. In practice, however, this capability can only be cost-effective in a relatively small, closed environment, such as within a hotel or an apartment building. In these situations, where the number of viewers at any given time is limited, it is possible to effectively dedicate a channel to each viewer and to begin a transmission of the movie over a viewer's channel upon receipt of a request to begin the movie.
This approach to video-on-demand services is not economically feasible in a broadcast environment, where the number of potential viewers is so large that the required bandwidth becomes cost-prohibitive. Consequently, broadcasters employ an approach that is labeled “near-video-on-demand”. In this approach, a popular movie is broadcast at multiple staggered start times over a limited number of channels. For instance, a two-hour movie can be broadcast over four channels at 30 minute intervals. Consequently, the viewer never has to wait more than 30 minutes for the start of the next presentation. With this approach, the number of channels occupied by a given movie is inversely proportional to the wait period. If 5 minutes is considered to be an acceptable wait time, a two-hour movie would require 24 channels. A one-minute wait time would occupy 120 channels.
In an effort to simulate true video-on-demand capabilities in a near-video-on-demand environment, a class of techniques has been developed which rely upon preliminary storage of part of the movie at the viewer's premises. One example of this technique is described in U.S. Pat. No. 5,884,141. In this technique, a desired movie is transmitted over multiple channels at staggered times, as in near-video-on demand. If the staggered presentation is to begin every 30 minutes, for example, the first 30 minutes of the movie, known as the leader, is automatically stored at the subscriber's premises. When a subscriber enters a request to view the movie, for example by pressing a “play” button on a set-top converter or a remote control unit, or by dialing a specified phone number, the first 30 minutes of the movie is replayed from the locally stored leader. During this time, the remaining portion of the movie, which occurs after the leader, begins to be stored from one of the channels allocated to the movie, and is replayed in a time-shifted fashion after the replay of the stored leader has completed.
Using this approach, the number of movies that can be viewed with substantially no wait time is determined by the amount of local storage capacity at the subscriber's premises. For example, several gigabytes of storage in the set-top converter unit are required to cache a 30-minute leader for each of ten select movies. If the subscriber desires to view any movie other than the ten whose leaders have been stored, the normal near-video-on-demand wait time would be encountered, e.g., 30 minutes.
While this approach can significantly reduce viewer wait times, relative to conventional and near-video-on-demand transmissions, it is highly dependent upon the amount of storage capacity that is available at the user's premises. It is desirable to provide video-on-demand capabilities in a broadcast environment with significantly reduced storage requirements at the subscriber's premises, and without a subscriber-hardware-based limit on the number of broadcast presentations that can be viewed with minimal wait times.
A broadcast technique which offers such a possibility is described in U.S. Pat. Nos. 5,751,336 and 5,936,659, as well as related publications “Pyramid Broadcasting for Video On Demand Service,” by S. Viswanathan and T. Imielinski, SPIE Proceedings, Vol. 2417, pp. 66-78, February 1995, and “Metropolitan Area Video-On-Demand Service Using Pyramid Broadcasting” by Viswanathan and Imielinski, Multimedia Systems, Vol. 4, pp. 197-208, 1996. In the technique described in these documents, each movie is divided into segments of increasing size, and each segment is repeatedly transmitted in an associated logical channel of the broadcast medium. In the disclosed implementations, each segment is approximately 2-2.5 times longer than the preceding segment. At the receiving end, once the first segment is received, all of the other segments are received in time, so that continuous viewing of the movie is possible.
While this technique provides improved results relative to the approaches described previously, the particular embodiments disclosed in the patents and related publications still require a significant amount of bandwidth. It is an objective of the present invention to improve upon the basic principles described in these references, and provide more efficient bandwidth utilization while minimizing viewer access time. It is a further objective to address some of the practical problems associated with the implementation of this technique which are not addressed in the references.